1. Field of the Invention
The present invention relates to a process for producing iodotrifluoromethane. More specifically, the present invention relates to a process for producing iodotrifluoromethane by reacting trifluoromethane with iodine in the presence of oxygen by use of a catalyst comprising a metal salt supported on a carbonaceous carrier.
2. Description of the Related Art
Iodotrifluoromethane is not only promising as a fire extinguisher substituting for Halon 1301 and Halon 1211, but also highly useful as a fluorine-containing intermediate compound for introducing a trifluoromethyl group in production of surfactants, agricultural chemicals, pharmaceuticals, and the like. Halon 1301, Halon 1211, and the like conventional fire extinguishers destroy the ozone layer, or cause global temperature rise by a greenhouse effect. Use of such extinguishers are being prohibited by environmental protection laws. On the other hand, the iodotrifluoromethane, which has a significantly shorter life in the air, causes negligibly the ozone layer destruction and the global temperature elevation. Therefore, the iodotrifluoromethane is promising for use as the fire extinguisher.
Several processes are known for production of iodotrifluoromethane. For example, J. Chem. Soc. 1951 p.584, and J. Org. Chem. 1967 p.833 disclose processes of reacting an alkali metal trifluoroacetate or silver trifluoroacetate with iodine; and J. Org. Chem. 1958 p.2016, and JP-A-2-262529 disclose processes of reacting a trifluoroacetyl halide with potassium iodide or lithium iodide.
Any of the above known methods employs expensive trifluoroacetic acid or its derivative as the source material. Moreover, use of alkali trifluoroacetate as the source material requires complete elimination of water including water of crystallization from the reaction system, and yet the yield is as low as about 70%. The expensive silver trifluoroacetate, although it gives a higher yield, is not necessarily advantageous to an industrial process.
JP-A-52-68110 discloses a process for producing iodotrifluoromethane in which trifluoromethane is reacted with iodine in the presence of a catalyst comprising an alkali metal salt or an alkaline earth metal salt supported by active carbon or active alumina. This process was replicated carefully by the inventors of the present invention. Consequently, it was found that, in the disclosed process, carbon deposition occurs, lowering significantly the catalyst activity in one or two days of the reaction, and the recovered iodine contains significant amount of a paste-like impurity estimated to be a high polymer. This recovered iodine cannot readily be purified, and complicated equipment is required for purification of the recovered iodine for recycling. Therefore, this process is not applicable to an industrial production.
As described above, the disclosed processes of production of iodotrifluoromethane from trifluoroacetic acid or its derivative are disadvantageous in that the source material is expensive, and use of more expensive silver salt of the trifluoroacetic acid is required for improving the yield. The conventional process of production of iodotrifluoromethane from trifluoromethane is also disadvantageous in that the catalyst life is short owing to carbon deposition, and the process requires a complicated equipment for eliminating a large amount of paste-like impurity from the recovered iodine for recycling it.
Therefore, a novel process for producing iodotrifluoromethane is demanded to overcome the disadvantages.
Under such circumstances, the inventors of the present invention made comprehensive studies on the process for producing iodotrifluoromethane by reaction of trifluoromethane with iodine. As the results, it was found that the reaction of trifluoromethane with iodine can be conducted with a long catalyst life in the presence of a catalyst comprising a metal salt supported on a carbonaceous carrier with coexistence of oxygen, and that the iodine which has not been converted to iodotrifluoromethane and by-product iodopentafluoroethane is recovered in a high purity without a paste-like impurity at a high recovery ratio and can be recycled without purification. The present invention is accomplished on the basis of the above findings.